Geographic Range

Tree lizards are found in the southwestern United States and northern Mexico, including southeastern California, southern Nevada, Utah, western Colorado, Arizona, New Mexico, southwest/central Texas, and Sonora, Sinaloa, Chihuahua, and North Coahuila. Tree lizards are predominantly found no higher than 2770 meters above sea level. (California Reptiles & Amphibians, 2009)

Habitat

Tree lizards are found at altitudes up to 2770 meters above sea level. They are common in riparian forested areas (mesquite, oaks, and cottonwoods), rocky terrain, sides of buildings and fence posts near streams, rivers and other bodies of freshwater. They are also found in desert habitats with or without trees. In treeless environments, these lizards take shelter in shrubs. ("Arizona-Sonora Desert Museum", 2009; California Reptiles & Amphibians, 2009)

Physical Description

Tree lizards are small lizards, ranging from 3.8 to 5.9 cm. They have a slim body and tail patterned with blotches and/or irregular crossbars with a variety of colorations ranging from black, dark brown, tan, and gray to match the local habitat. Down the middle of the back there are two bands of larger scales running the length of the body. The base of their tails is usually a rusty color. Adult males have brightly colored patches on the ventral surface. The sides of the belly are blue to blue-green and have a metallic sheen. An additional colored patch found on the throats of males, known as a dewlap, can be green, blue-green, orange, or yellow, whereas females have a white underbelly and throat color in white, orange, or yellow. ("Arizona-Sonora Desert Museum", 2009; California Reptiles & Amphibians, 2009)

Development

Tree lizard sex determination is not temperature-dependent and females produce clutches of eggs as opposed to giving live birth.
Development of a clutch takes 30 days from the time a female lays and buries her eggs. After hatching, rapid growth occurs during the fall and spring of the first year.
Levels of progesterone and testosterone have been correlated with aggressive behavior and dewlap coloration in male tree lizards. Levels of these two chemicals peak in offspring on the day of hatching and again 60 days post-hatching. An increase in these chemicals produces more territorial and aggressive behaviors as well as an orange-blue dewlap coloration in adults. (Jennings, et al., 2004; Jennings, et al., 2004)

Reproduction

Prior to reproduction, females establish a territory. Females remain in their territory and mate with males who have overlapping territories. A polygamous mating system is common where populations are dense. As many as 4 males and 7 females have been observed to inhabit a single tree. In a case where multiple males inhabit the same territory, a dominance tyranny will be established by one male. Subordinates to this male will not follow any direct hierarchy. A study conducted by Deslippe, et. al. (1990), showed that the single dominant male was responsible for 91.5% of the mating attempts and all successful copulations. ("Arizona-Sonora Desert Museum", 2009; Deslippe, et al., 1990; Disleppe, et al., 1990)

If there are multiple males, the color of their dewlap correlates with dominance in short term encounters. It has been hypothesized that females use dewlap color in mate selection. However, in mate selection studies, dewlap color has not been shown to impact selection. Studies have also been done with other male morphological features and behaviors, yet none have been shown to significantly alter female mate selection in tree lizards. (Smith and Zucker, 1997)

The reproductive season for tree lizards lasts from March to August. Both males and females reach sexual maturity at about 45mm SVL (Snout-Vent Length) or by May to June of the year following hatching. During a single mating season tree lizards can produce 1 to 6 clutches (3 on average), producing 2 to 13 (7.1 on average) eggs per clutch. One study observed hatchlings 50 days after the first clutch was laid. The time in oviposition and the clutch size can vary greatly across range. Younger females produce fewer eggs per clutch than older ones. (Deslippe, et al., 1990; NatureServe Explorer, 2009; Tinkle and Dunham, 1983)

Females are normally sedentary during the breeding season, which may decrease predation and conserve energy. This may be an adaptive strategy to ensure the survival of offspring. A week prior to ovoposition, females show increased activity, possibly to find a suitable clutch site. Males remain active throughout the breeding season. (Smith and Zucker, 1997)

The ideal location in which to lay a clutch is under rocks, in the dirt, or underground. The female digs the area intensively two days prior to egg laying, taking time to rest and bask in the heat. The chamber is dug 9 to 11 cm deep. Once eggs are laid, she covers them up with sand or dirt, completely filling the chamber. There has been no known female-to-female aggression displayed during this time; in fact, they have been observed basking together. (Deslippe, et al., 1990)

The only parental investment in the young is demonstrated by the female prior to egg-laying. She finds an ideal location to lay her clutch (requiring moisture and warm temperatures of the sand or soil), digs a single chamber per clutch, lays her eggs, fills the chamber back up and leaves. Separate holes are dug for additional clutches and significant nutritional resources are necessary to supply eggs with yolk to fuel development. (Deslippe, et al., 1990; NatureServe Explorer, 2009)

Despotic hierarchies develop among male tree lizards in which one male, usually the heaviest, will dominate all the other males in a single area. There is little female-female interaction due to individual territories of the females. This does not allow a hierarchy to form among female tree lizards.
Tree lizards aggregate in the winter to hibernate. Aggregated tree lizards can be found in hibernacula as early as mid November and as late as the end of February.
A tree lizard may remain in a single tree unless searching for better resources. Tree lizards are known to climb high into trees for protection from predators. Hunting for insects occurs at dawn and into the late afternoon. (Ivanyi, 2004; Tinkle and Dunham, 1983)

Home Range

Studies indicate high variability in the size of home ranges in tree lizards. Male tree lizards have an average home range size of 154 square meters. Female tree lizards, on average, have smaller home range sizes of 109 square meters. Two-dimensional home ranges average 70 square meters in males and 30 square meters in females. Some studies have shown that the home range size varies throughout the year. This variance is not due to migration. (NatureServe Explorer, 2009)

Communication and Perception

Lizards, in general, communicate predominantly through visual and chemical signals. Typically, visual signals between lizards are used in intra- and inters-exual communication, whereas chemical signals are used for detection of kin, familiar individuals, and conspecifics. In tree lizards, the use of chemical signals does not seem to play a role in reproductive behavior. Visual signals, such as the male’s brightly colored underbelly, dewlap, and sometimes dorsal coloring play an important role in male-male interactions and tend to aid in establishing a dominance hierarchy. Physical displays, such as a 4-legged pushup, are also a component in tree lizard communication.
Chemoreceptive behaviors include tongue-flicking where the tongue is extended, though it may not touch anything, or nose-tapping where the rostrum touches an object. (Quinn and Hews, 2005)

Economic Importance for Humans: Positive

Humans may benefit from the control of insect populations due to predation by tree lizards. No economic importance has been reported.

Positive Impacts

research and education

controls pest population

Economic Importance for Humans: Negative

Tree lizards are not known to pose any harm or cost to humans or their pets.

Conservation Status

Tree lizards are not currently threatened and their populations are predicted to remain stable. There are no current or foreseen threats to this species. The estimated total global population is between 100,000 to 1,000,000 individuals. (NatureServe Explorer, 2009)

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

arboreal

Referring to an animal that lives in trees; tree-climbing.

carnivore

an animal that mainly eats meat

chaparral

Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.

chemical

uses smells or other chemicals to communicate

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

diurnal

active during the day, 2. lasting for one day.

dominance hierarchies

ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

hibernation

the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.

insectivore

An animal that eats mainly insects or spiders.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

polygynous

having more than one female as a mate at one time

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

scent marks

communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them

scrub forest

scrub forests develop in areas that experience dry seasons.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

tactile

uses touch to communicate

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

vibrations

movements of a hard surface that are produced by animals as signals to others

Jennings, D., D. Painter, M. Moore. 2004. Role of the Adrenal Gland in Early Post-Hatching Differentiation of Alternative Male Phenotypes in the Tree Lizard. General and Comparative Endocrinology, 135/1: 81-89.

Miles, D. 1994. Population Differentiation in Locomotor Performance and the Potential Response of a Terrestrial Organism to Global Environmental Change. American Zoologist, 34/3: 422-436.

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This material is based upon work supported by the
National Science Foundation
Grants DRL 0089283, DRL 0628151, DUE 0633095, DRL 0918590, and DUE 1122742. Additional support has come from the Marisla Foundation, UM College of Literature, Science, and the Arts, Museum of Zoology, and Information and Technology Services.